Overview of This is Your Brain on Hormones
This Radiolab episode explores a long-running question about whether hormones physically change the brain—and if so, how. Reporter Molly Webster and neuroscientist Emily Jacobs walk through new imaging research showing that the brain is not static across the menstrual cycle or the day. Instead, it appears to shift in connectivity and even structure as hormones rise and fall. The episode also challenges the stereotype that “women are hormonal” in a uniquely unstable way by showing that men’s brains are also cycling with hormones, just on a different rhythm.
Main question: Do hormones change the brain?
The episode starts with the idea Molly had heard years earlier: that the brain changes shape or makeup across the menstrual cycle. Emily Jacobs explains that the old research was mostly indirect and static—one brain scan, one blood draw, one moment in time. That approach misses the basic fact that hormones are dynamic and rhythmic.
Hormones are framed as the body’s broadcast system:
- They’re chemical messengers released by glands like the ovaries, testes, thyroid, and adrenals.
- They travel through the bloodstream.
- They affect nearly every cell, including the brain.
The big scientific shift, according to Emily, was realizing that if you want to understand hormones, you have to track change over time.
Key findings from the experiments
Laura Pritchett’s 28-day self-study
Emily’s lab worked with graduate student Laura Pritchett, who volunteered to be scanned daily across an entire menstrual cycle.
Each day, Laura:
- gave saliva and blood samples,
- underwent MRI scans,
- completed brain tasks,
- tracked her mood.
The results were striking:
- When estradiol peaked around ovulation, the brain became more functionally connected—different regions were “talking” to each other more.
- When estrogen dropped and progesterone became dominant in the days before menstruation, those connections became less synchronized.
- In a high-resolution look at the hippocampus—a memory-related region—parts of the structure actually grew and shrank across the cycle.
To test causality, Laura then used hormonal birth control that suppressed progesterone. When they repeated the scan:
- the progesterone-related hippocampal changes were obliterated,
- strongly suggesting the changes were driven by hormone cycling.
Pavel’s daily hormone study
Emily and Laura then studied Pavel, Laura’s partner, to see whether similar effects happen in men.
They scanned him:
- in the morning and evening,
- over multiple days,
- while tracking hormones like testosterone, estrogen, and progesterone.
They found a similar pattern:
- High hormone levels corresponded to more interconnected brain activity.
- Lower hormone levels corresponded to less connectivity.
The difference is that men’s hormones were found to fluctuate more on a daily circadian rhythm, especially testosterone, which is high in the morning and lower at night.
What the episode argues
The central takeaway is not that one state is “better” or “worse,” but that the brain is built to change.
Emily argues:
- hormones help create neuroplasticity, the brain’s ability to adapt and learn,
- hormonal cycles may actually provide an organizing rhythm for the brain,
- what has often been labeled as “noise” may instead be a feature that supports stability and function.
In other words, the brain’s changing state may not be a flaw—it may be part of how it works.
A more nuanced view of mood and behavior
The episode is careful not to overclaim. Even though hormone-linked brain changes are real, the scientists say they cannot directly map them onto individual mood or behavior in a simple way.
Why not?
- Hormones interact with many systems, including dopamine.
- The same hormonal change could feel good in one person and bad in another.
- Bodies and brains are highly individualized.
Still, Laura’s own mood tracking suggested a correlation between rising progesterone and increases in negative affect, showing how personal the experience can be.
Bigger implications: hormones, stress, and resilience
The episode also briefly touches on newer research suggesting:
- high estrogen plus stress may create PTSD-like effects in animals,
- low estrogen periods may provide a kind of resilience or “armor” against stress.
This is presented as early and still speculative, but it supports the broader theme: hormones may shape not just mood, but how the brain responds to stress and learns from experience.
The episode’s broader message
The story pushes back on sexist assumptions that women are uniquely unstable or “hormonal.” Instead, it argues:
- all humans have hormones,
- all brains are rhythmic,
- and hormonal fluctuation is a normal, essential part of biology.
A key line of thought in the episode: maybe the menstrual cycle is not a source of noise, but a source of stability and structure.
Resources and notable details
- The researchers mention making their data publicly available on OpenNeuro.
- The episode highlights the foundational work of Catherine Woolley on sex hormones and the brain.
- It also points toward future tech like continuous hormone monitors, which could reveal hormone dynamics in real time the way glucose monitors do for blood sugar.
Bottom line
This episode reframes hormones as powerful, rhythmic organizers of brain function rather than just mood-disrupting chemicals. It shows that:
- brains change across the menstrual cycle,
- brains also change across the day in men,
- these changes are real, measurable, and likely important,
- but their exact effects on behavior and cognition are still an open scientific frontier.